Solid state image pickup device comprising a charge transfer device such as a charge coupled device (hereinafter referred to as a CCD) are classfied broadly into the frame transfer type and the interline transfer type, and there are advantages common to both types that they can be constructed as devices of small size and light weight and can be operative with low power consumption and with high reliability. Accordingly, the solid state image pickup devices comprising CCD image pickup devices are image pickup devices which are expected to be successful. However, previously proposed CCD image pickup devices have encountered several problems such as the undesirable phenomena called "blooming" and "smear".
There have been proposed some measures for reducing deterioration in the quality of a picture reproduced in response to an image pickup signal output from the CCD image pickup device, which are caused by the blooming and the smear. For example, it is considerably effective for reducing deterioration in the quality of the reproduced picture caused by the blooming to provide an overflow drain in the CCD image pickup device, which is operative to drain superfluous charges overflowing from photo-sensing elements contained during the device in a light receiving period. However, such an overflow drain provided in the CCD image pickup device would raise disadvantages such as the area of each photo-sensing element is reduced or the degree of integration of the photo-sensing elements is reduced, so that photo-sensitivity and image-resolvability of the device are degraded.
Accordingly, a CCD image pickup device which can suppress deteriorations in the quality of a picture obtained in response to an image pickup signal output therefrom caused by the blooming and the smear, has been proposed which have a photo-sensing and vertical transfer portion and a horizontal transfer portion, both of which are provided in the form similar to those employed in a CCD image pickup device of the interline transfer type. A storage portion provided in a form similar to that used in a CCD image pickup device of the frame transfer type between the photosensing and vertical transfer portion and the horizontal transfer portion, wherein signal charges in vertical transfer portions contained in the photo-sensing and vertical transfer portion are transferred to the storage portion at high speed and each of the vertical transfer portions which are vacant acts as the overflow drain during the light receiving period.
Such a solid state image pickup device developed from the CCD image pickup device of the interline transfer type is referred to as a solid state image pickup device of the hybrid type hereinafter. In the solid state image pickup device of the hybrid transfer type, signal charges read out to the vertical transfer portions from photodetectors contained also in the photo-sensing and vertical transfer portion are transferred to the storage portion at high speed, and the signal charges transferred to the storage portion are further transferred to the horizontal transfer portion from the storage portion in turn during every period corresponding to a horizontal blanking period. Each of the vertical transfer portions, from which the signal charges have been transferred to the storage period so as to vacate them, acts as the overflow drain for excessive charges overflowing from the photodetectors and needless charges leaking into the vertical transfer portions, during the light receiving period. Then, prior to a read out period, in which the signal charges stored in the photodetectors are read out to the vertical transfer portions, which occur after the light receiving period, unnecessary charges remaining in the vertical transfer portions are transferred or swept out. Consequently, the signal charges transferred to the storage portion from the vertical transfer portions are prevented from containing unnecessary charges, and further, since the charge transfer of the signal charges to the storage portion in the vertical transfer portions is carried out at high speed within a relatively short period, undesirable charges will not leak into the signal charges during the period in which the signal charges are transferred to the storage portion and are reduced. As a result of, an image pickup signal output, with which a reproduced picture can be obtained with less deterioration in the quality caused due to the blooming and the smear, can be obtained by the solid state image pickup device of the hybrid transfer type.
However, in such a device of the hybrid transfer type as described above, the charge transfer for sweeping out the unnecessary charges in the vertical transfer portions is required to be performed in the direction opposite to the direction of the charge transfer of the signal charges to the storage portion and this results in the disadvantage that the configuration of the driving mechanism for causing the vertical transfer portions and the storage portion to perform the charge transfers becomes complicated. In addition, it is also required for the photodetectors and the vertical transfer portions to have superfluous charge capacity for handling the excessive charges during the period in which the charge transfer is performed in the vertical transfer portions and this results in another disadvantage in that only a portion, for example, less than fifty percents of the maximum charge which can be handled by the device can be used as the signal charges.
Accordingly, it is an object of the present invention to provide a novel solid state image pickup device formed in the hybrid transfer type so as to have the advantages generally incidental to a device of the hybrid transfer type and which is improved in configuration and operation so that the charge transfer at high speed for sweeping out unnecessary charges, which is done in the previously proposed device of the hybrid transfer type, is not required to be performed and therefore the configuration of the driving mechanism for causing vertical transfer and storage transfers is simplified, and the signal charge capacity thereof is increased and therefore and dynamic range of an image pickup signal output is increased.